U.S. patent application number 15/368794 was filed with the patent office on 2017-06-08 for laser reseal including optimized intensity distribution.
The applicant listed for this patent is Robert Bosch GmbH. Invention is credited to Mawuli Ametowobla, Alexander Ilin, Philip Kappe, Jochen Reinmuth.
Application Number | 20170157710 15/368794 |
Document ID | / |
Family ID | 58723010 |
Filed Date | 2017-06-08 |
United States Patent
Application |
20170157710 |
Kind Code |
A1 |
Ilin; Alexander ; et
al. |
June 8, 2017 |
LASER RESEAL INCLUDING OPTIMIZED INTENSITY DISTRIBUTION
Abstract
A method is described for manufacturing a micromechanical
component including a substrate and a cap connected to the
substrate, the cap, together with the substrate, enclosing a first
cavity, a first pressure prevailing and a first gas mixture having
a first chemical composition being enclosed in the first cavity. An
access opening connecting the first cavity to surroundings of the
micromechanical component is formed in the substrate or in the cap.
The first pressure and/or the first chemical composition is
adjusted in the first cavity. The access opening is sealed by
introducing energy or heat into an absorbing part of the substrate
or of the cap with the aid of a laser. The introduction of the
energy or heat is controlled with the aid of a laser beam, which
includes a spatial laser pulse expansion.
Inventors: |
Ilin; Alexander;
(Ludwigsburg, DE) ; Reinmuth; Jochen; (Reutlingen,
DE) ; Ametowobla; Mawuli; (Stuttgart, DE) ;
Kappe; Philip; (Hildesheim, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Robert Bosch GmbH |
Stuttgart |
|
DE |
|
|
Family ID: |
58723010 |
Appl. No.: |
15/368794 |
Filed: |
December 5, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B23K 2103/50 20180801;
B23K 2101/42 20180801; B23K 26/206 20130101; B23K 2103/54 20180801;
B23K 26/0622 20151001; B23K 2101/36 20180801; B23K 26/324 20130101;
B23K 26/0604 20130101 |
International
Class: |
B23K 26/20 20060101
B23K026/20 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 8, 2015 |
DE |
102015224500.4 |
Claims
1. A method for manufacturing a micromechanical component including
a substrate and a cap connected to the substrate, the cap, together
with the substrate, enclosing a first cavity, a first pressure
prevailing and a first gas mixture having a first chemical
composition being enclosed in the first cavity, the method
comprising: in a first method step, forming, in the substrate or
the cap, an access opening connecting the first cavity to
surroundings of the micromechanical component; in a second method
step, adjusting, in the first cavity, at least one of the first
pressure and the first chemical composition; in a third method
step, sealing the access opening by introducing energy or heat into
an absorbing part of the substrate or the cap, with the aid of a
laser, wherein the introduction of the energy or heat is controlled
with the aid of a laser beam, which includes a spatial laser pulse
expansion extending along a surface of the substrate or the cap
facing away from the first cavity and extending in parallel to a
main extension plane of the substrate, and a laser pulse intensity
to minimize internal stresses in the substrate or in the cap.
2. The method as recited in claim 1, wherein the introduction of
the energy or the heat is controlled with the aid of the laser beam
in such a way that the laser pulse expansion includes a first laser
pulse expansion area having at least one first laser pulse
intensity and a second laser pulse expansion area having at least
one second laser pulse intensity, a projection of the first laser
pulse expansion area on the main extension plane and a projection
of the access opening on the main extension plane at least
partially overlapping.
3. The method as recited in claim 2, wherein the introduction of
the energy or heat is controlled with the aid of the laser beam in
such a way that a projection of the first laser pulse expansion
area on the main extension plane and a projection of the second
laser pulse expansion area on the main extension plane are spaced
apart from one another.
4. The method as recited in claim 2, wherein the introduction of
the energy or heat is controlled with the aid of the laser beam in
such a way that a projection of the second laser pulse expansion
area on the main extension plane and a projection of the access
opening on the main extension plane are spaced apart from one
another.
5. The method as recited in claim 2, wherein the introduction of
the energy or heat is controlled with the aid of the laser beam in
such a way that a first material area of a first absorbing area of
the absorbing part of the substrate or the cap enters a liquid
aggregate state as a result of the first laser pulse intensity of
the first laser pulse expansion area, a second material area of a
second absorbing area of the absorbing part of the substrate or the
cap entering a liquid aggregate state or remaining in a solid
aggregate state as a result of the second laser pulse intensity of
the second laser pulse expansion area.
6. The method as recited in claim 1, wherein the introduction of
the energy or heat is controlled with the aid of the laser beam in
such a way that the spatial laser pulse expansion is formed over an
entire area or as a section area of a hollow cylinder extending
perpendicularly in relation to the longitudinal axis of the hollow
cylinder, the longitudinal axis being coincident with a center
point of the access opening.
7. The method as recited in claim 2, wherein the introduction of
the energy or heat is controlled with the aid of the laser beam in
such a way that the second laser pulse expansion area includes a
first subarea and a second subarea, a projection of the first
subarea on the main extension plane and a projection of the second
subarea on the main extension plane being spaced apart from one
another.
8. The method as recited in claim 7, wherein the introduction of
the energy or heat is controlled with the aid of the laser beam in
such a way that the first subarea and the second subarea are formed
rotationally-symmetrically and in parallel to the surface.
9. The method as recited in claim 7, wherein the introduction of
the energy or heat is controlled with the aid of the laser beam in
such a way that the second laser pulse expansion area includes
further subareas, the further subareas being formed
rotationally-symmetrically and in parallel to the surface and being
situated rotationally-symmetrically around the access opening and
in parallel to the surface with the first subarea and the second
subarea.
10. A micromechanical component, comprising: a substrate; and a cap
connected to the substrate, the cap, together with the substrate,
enclosing a first cavity, a first pressure prevailing and a first
gas mixture having a first chemical composition being enclosed in
the first cavity, the substrate or the cap including a sealed
access opening; wherein the substrate or the cap includes a
material area which solidifies and seals the access opening after a
controlled introduction of energy or heat into an absorbing part of
the substrate or the cap with the aid of a laser beam, which
includes a spatial laser pulse expansion extending along a surface
of the substrate or the cap facing away from the first cavity and
extending in parallel to a main extension plane of the substrate,
and a laser pulse intensity to minimize internal stresses in the
substrate or in the cap.
Description
CROSS REFERENCE
[0001] The present application claims the benefit under 35 U.S.C.
.sctn.119 of German Patent Application No. DE 102015224500.4 filed
on Dec. 8, 2015, which is expressly incorporated herein by
reference in its entirety.
BACKGROUND INFORMATION
[0002] A method is described in PCT Application No. WO 2015/120939
A1 in which, when a particular internal pressure is desired in a
cavity of a micromechanical component or a gas mixture having a
certain chemical composition is to be enclosed in the cavity, the
internal pressure or the chemical composition is frequently
adjusted during capping of the micromechanical component or during
the bonding process between a substrate wafer and a cap wafer.
During capping, for example, a cap is connected to a substrate,
whereby the cap and the substrate together enclose the cavity. By
adjusting the atmosphere or the pressure and/or the chemical
composition of the gas mixture present in the surroundings during
capping, it is thus possible to adjust the particular internal
pressure and/or the particular chemical composition in the
cavity.
[0003] With the aid of the method described in PCT Application No.
WO 2015/120939 A1, an internal pressure may be adjusted in a
targeted way in a cavity of a micromechanical component. It is in
particular possible with the aid of this method to manufacture a
micromechanical component including a first cavity, a first
pressure and a first chemical composition being adjustable in the
first cavity, which differ from a second pressure and a second
chemical composition at the time of capping.
[0004] In the method for targeted adjusting of an internal pressure
in a cavity of a micromechanical component according to PCT
Application No. WO 2015/120939 A1, a narrow access channel to the
cavity is created in the cap or in the cap wafer, or in the
substrate or in the sensor wafer. Subsequently, the cavity is
flooded with the desired gas and the desired internal pressure via
the access channel. Finally, the area around the access channel is
locally heated with the aid of a laser, the substrate material
liquefies locally and hermetically seals the access channel during
solidification.
[0005] In rotation rate sensors, for example, a very low pressure
is enclosed, which is less than 1 mbar, for example. This is the
case because a part of the movable structures is driven resonantly
in rotation rate sensors. At low pressure, an oscillation may be
excited very easily using relatively low stresses as a result of
the slight damping.
[0006] In acceleration sensors, in contrast, it is not desirable
for the sensor to begin to oscillate, which would be possible upon
application of an external acceleration. The sensors are therefore
operated at higher internal pressure. The internal pressure of an
acceleration sensor is, for example, 500 mbar.
SUMMARY
[0007] It is an object of the present invention to provide a method
for manufacturing a micromechanical component which is mechanically
robust and has a long service life compared to the related art, in
a simple and cost-effective manner compared to the related art. It
is a further object of the present invention to provide a
micromechanical component which is compact, mechanically robust and
has a long service life compared to the related art. According to
the present invention, this applies, in particular, to a
micromechanical component that includes one (first) cavity. With
the aid of the method according to the present invention and the
micromechanical component according to the present invention, it is
furthermore also possible to implement a micromechanical component
in which a first pressure and a first chemical composition may be
adjusted in the first cavity, and a second pressure and a second
chemical composition may be adjusted in a second cavity. For
example, such a method is provided for manufacturing
micromechanical components, for which it is advantageous if a first
pressure is enclosed in a first cavity and a second pressure is
enclosed in a second cavity, the first pressure being different
from the second pressure. This is the case, for example, when a
first sensor unit for rotation rate measurement and a second sensor
unit for acceleration measurement are to be integrated into a
micromechanical component.
[0008] The object may be achieved in accordance with example
embodiments of the present invention by providing that the
introduction of the energy or heat is controlled with the aid of a
laser beam, which includes a spatial laser pulse expansion, which
extends essentially along a surface of the substrate or the cap
facing away from the first cavity and extending essentially in
parallel to a main extension plane of the substrate, and a laser
pulse intensity, to minimize internal stresses in the substrate or
in the cap.
[0009] In this way, a method for manufacturing a micromechanical
component is provided in a simple and cost-effective way, using
which the introduction of the energy or heat is controllable with
the aid a laser beam including a spatial laser pulse expansion and
a laser pulse intensity, to minimize internal stresses in the
substrate or in the cap. This advantageously enables the energy or
heat to be introduced in a targeted spatial way into the substrate
or into the cap. Therefore, a first transition of the material area
from the solid into the liquid aggregate state and a second
transition, which follows the first transition chronologically, of
the material area from the liquid into the solid aggregate state in
the substrate or in the cap may be controlled in a spatially
targeted way. In addition, as a result of the spatial distribution
of the energy or heat using the method according to the present
invention, areas of the substrate or the cap adjoining the material
area of the substrate or the cap may be brought to an increased
temperature in comparison to the related art in a spatially
targeted way. Therefore, the temperature gradients in the substrate
or in the cap, in particular in the area of the access opening, may
be reduced in comparison to the related art. This enables the
thermal expansion in the event of a temperature increase and/or the
thermal shrinking in the event of a temperature reduction of
adjacent areas in the substrate or in the cap, in particular in the
area of the access opening, to be adapted to one another and
therefore the mechanical stresses or internal stresses occurring in
the area of the sealed access opening, in particular due to the
cooling process after the third method step, to be able to be
reduced in comparison to the related art. The dissipation or
reduction of locally occurring stresses or tensions is in
particular advantageous because the resistance to cracking is
therefore increased in comparison to the related art and therefore
the probability of a component failure immediately after the
sealing of the access opening, during the further processing of the
micromechanical component, or during the product service life may
be reduced in comparison to the related art. By avoiding cracks, in
particular a hermetic seal of the access opening is enabled and
therefore the probability of a restriction of the functionality of
the micromechanical component due to a leaking seal of the access
opening is reduced in comparison to the related art.
[0010] Using the method according to the present invention, in
particular temperature gradients between the only recently
solidified material area and the material surrounding the material
area may be reduced in comparison to the related art by spatially
targeted increase of the temperature in the substrate or in the
cap. In particular, these temperature gradients at the time of the
solidification of the material area may be reduced chronologically
shortly after the solidification of the material area. This
advantageously enables the thermal shrinking of the material area
to substantially correspond to the thermal shrinking of the
material enclosing the material area or the two thermal shrinkings
to be adapted to one another. This advantageously enables the
mechanical stresses occurring in the area of the sealed access
opening, in particular chronologically after the cooling of the
material area, to be reduced in comparison to the related art.
[0011] According to the present invention, temperature gradients at
a time at which the material area is in a liquid aggregate state or
is in the melted state are less critical, because the material area
is essentially stress-free at this time. According to the present
invention, however, it is provided, for example, that the
temperature gradients are also reduced in comparison to the related
art at the time at which the material area is in a liquid aggregate
state. In particular, the present invention avoids or reduces
stresses from building chronologically after the solidification of
the material area by the fact that the material area which is only
recently solidified is hotter than the material surrounding the
material area and thus experiences a stronger/different thermal
expansion during the cooling procedure than the colder material
surrounding the material area. It is provided according to the
present invention that the temperature gradient in the material or
in the substrate or in the cap is kept as small as possible during
the solidification of the material area and during the cooling, so
that the mechanical stresses remaining in the component after
cooling are as small as possible.
[0012] A further advantage of the method according to the present
invention is that the movement of displacements is thermally
activatable with the aid of the targeted spatial introduction of
the energy or heat into the substrate or into the cap. It is
therefore advantageously possible that the substrate or the cap is
plastically deformable at least partially or at least partially
locally in the area of the access opening, in particular
chronologically after the second transition, by thermally activated
displacement movements or by facilitated displacement movements.
Therefore, locally occurring stresses or stress spikes may be
reduced or dissipated in comparison to the related art by plastic
deformation with the aid of the targeted introduction of the energy
or heat.
[0013] The method according to the present invention is also
advantageous if surfaces of sensors or sensor cores are provided
with organic coatings, which prevent moving structures from
sticking to one another, and if these organic coatings degrade and
are no longer fully effective at the high temperatures in the
bonding method, for example. At least partial release of the
organic layers into the cavity and therefore increased internal
pressure after sealing the MEMS element may be counteracted in a
simple and cost-effective way using the method according to the
present invention.
[0014] In addition, the method according to the present invention
is also advantageous, for example, in relation to a method in which
different pressures p1/p2 are required in a cavity of a rotation
rate sensor p1 and in a cavity of an acceleration sensor p2, a high
pressure which is initially enclosed in both cavities subsequently
being brought to a low pressure in the cavity of the rotation rate
sensor with the aid of a getter by activating the getter via a
temperature step in the cavity of the rotation rate sensor. The
method according to the present invention is comparatively simple
and cost-effective in relation to such a method.
[0015] Furthermore, the method according to the present invention
is advantageous if the sealing of a MEMS structure situated in the
first cavity using a cap wafer is carried out at high temperatures,
for example, using a seal glass as the connecting material or using
various other bonding materials or bonding systems, for example,
eutectic aluminum-germanium (AlGe) or copper-tin-copper (CuSnCu)
systems. Even if the bonding method is carried out under vacuum and
at high temperatures, gases vaporize from the bonding system at
high temperature and cause a residual pressure in the cavity, which
prevails independently of the very low pressure during the bonding
method in the bonding chamber and therefore in the cavity. This
residual pressure may be significantly reduced in relation to the
related art using the method according to the present
invention.
[0016] In particular, the method according to the present invention
is also advantageous, for example, if outgassing of noble gases or
other gases from the wafers or from the substrate or from the cap
or from a bonding layer takes place during the bonding process, if
the noble gases or other gases may be pumped only poorly or not at
all by the getter, because the first pressure may be adjusted
chronologically after the bonding process with the aid of the
access opening using the method according to the present invention.
Therefore, such outgassing may be effectively counteracted using
the method according to the present invention. This is advantageous
because outgassing of noble gases or other gases which may be
pumped only poorly or not at all by the getter would restrict the
minimum pressure to be achieved and even at higher pressures, this
outgassing could cause strong, undesired scattering of the internal
pressure.
[0017] The laser beam is to be understood in the context of the
present invention as electromagnetic radiation which is emitted
continuously or non-continuously by a laser. The laser may be, for
example, a pulsed laser or a continuous wave laser. In addition, it
is provided according to the present invention that the continuous
wave laser is operated so that the electromagnetic radiation is
continuously emitted or is continuously incident on the absorbing
part of the substrate or the cap. In addition, it is provided that
the electromagnetic radiation is incident on the absorbing part of
the substrate or the cap and is at least partially absorbed
thereby.
[0018] According to the present invention, a laser beam including a
spatial laser pulse expansion and a laser pulse intensity is to be
understood to mean that the laser beam includes a spatial intensity
distribution, the laser pulse intensity within the spatial laser
pulse expansion being greater than zero or greater than a minimum
laser pulse intensity. In other words, the spatial laser pulse
expansion is defined in such a way that the laser pulse intensity
spatially within the laser pulse expansion is greater than zero or
is greater than the minimum laser pulse intensity, and that the
laser pulse intensity spatially outside the laser pulse expansion
is equal to zero or is less than the minimum laser pulse intensity.
In the context of the present invention, the laser pulse expansion
and the laser pulse intensity is meant essentially along the
surface of the substrate or the cap facing away from the first
cavity and extending essentially in parallel to the main extension
plane of the substrate.
[0019] The term "micromechanical component" is to be understood in
the context of the present invention to mean that the term includes
both micromechanical components as well as microelectromechanical
components.
[0020] The present invention is preferably provided for a
micromechanical component including a cavity or for its
manufacture. However, the present invention is also provided, for
example, for a micromechanical component including two cavities or
including more than two, i.e., three, four, five, six or more than
six, cavities.
[0021] The access opening is preferably sealed with the aid of a
laser by introducing energy or heat into a part of the substrate or
of the cap that absorbs this energy or this heat. In this case,
energy or heat is preferably introduced chronologically in
succession into the respective absorbing part of the substrate or
of the cap of multiple micromechanical components, which are
manufactured together, for example, on one wafer. Alternatively,
however, a chronologically parallel introduction of the energy or
heat into the respective absorbing part of the substrate or of the
cap of multiple micromechanical components is also provided, for
example, using multiple laser beams or laser devices.
[0022] Advantageous embodiments and refinements of the present
invention are described herein with reference to the figures.
[0023] According to one preferred refinement, it is provided that
the cap, together with the substrate, encloses a second cavity, a
second pressure prevailing and a second gas mixture having a second
chemical composition being enclosed in the second cavity.
[0024] According to one preferred refinement, it is provided that
the introduction of the energy or heat is controlled with the aid
of the laser beam in such a way that the laser pulse expansion
includes a first laser pulse expansion area having at least one
first laser pulse intensity and a second laser pulse expansion area
having at least one second laser pulse intensity, a projection of
the first laser pulse expansion area on the main extension plane
and a projection of the access opening on the main extension plane
at least partially overlapping. This advantageously enables the
absorbing part to be spatially allocated with the aid of the first
laser pulse intensity and the second laser pulse intensity over the
first laser pulse expansion area and the second laser pulse
expansion area. It is thus advantageously enabled for the material
area to only enter a liquid aggregate state in certain areas of the
absorbing part.
[0025] The laser pulse expansion including a first laser pulse
expansion area having at least one first laser pulse intensity and
a second laser pulse expansion area having at least one second
laser pulse intensity is to be understood according to the present
invention to mean that the first laser pulse intensity within the
first laser pulse expansion area and the second laser pulse
intensity within the second laser pulse expansion area are each
greater than zero or greater than a minimum laser pulse intensity.
In addition, this is to be understood to mean that the first laser
pulse intensity outside the first laser pulse expansion area and
the second laser pulse intensity outside the second laser pulse
expansion area are each equal to zero or are less than a minimum
laser pulse intensity.
[0026] According to one preferred refinement, it is provided that
the introduction of the energy or heat is controlled with the aid
of the laser beam in such a way that a projection of the first
laser pulse expansion area on the main extension plane and a
projection of the second laser pulse expansion area on the main
extension plane are spaced apart from one another. This
advantageously enables the introduction of the energy or heat to be
carried out in areas which are spatially separated from one another
in the substrate or in the cap.
[0027] According to one preferred refinement, it is provided that
introduction of the energy or heat is controlled with the aid of
the laser beam in such a way that a projection of the second laser
pulse expansion area on the main extension plane and a projection
of the access opening on the main extension plane are spaced apart
from one another. This advantageously enables energy or heat to be
introduced into an area of the substrate or the cap spaced apart
from the access opening.
[0028] According to one preferred refinement, it is provided that
the introduction of the energy or heat is controlled with the aid
of the laser beam in such a way that a first material area of a
first absorbing area of the absorbing part of the substrate or the
cap enters a liquid aggregate state as a result of the first laser
pulse intensity of the first laser pulse expansion area, a second
material area of a second absorbing area of the absorbing part of
the substrate or the cap entering a liquid aggregate state or
remaining in a solid aggregate state as a result of the second
laser pulse intensity of the second laser pulse expansion area.
This advantageously enables local mechanical stresses, in
particular compressive stresses, to be generated in the substrate
or the cap, which counteract stresses, in particular tensile
stresses, occurring in the area of the access opening.
[0029] According to one preferred refinement, it is provided that
the introduction of the energy or heat is controlled with the aid
of the laser beam in such a way that the spatial laser pulse
expansion is formed over the entire area or as a section area of a
hollow cylinder extending perpendicularly in relation to the
longitudinal axis of the hollow cylinder, the longitudinal axis
being essentially coincident with the center point of the access
opening. This advantageously enables the energy or heat to be
introduced into the substrate or cap in a particularly targeted
way.
[0030] According to one preferred refinement, it is provided that
the introduction of the energy or heat is controlled with the aid
of the laser beam in such a way that the second laser pulse
expansion area includes a first subarea and a second subarea, a
projection of the first subarea on the main extension plane and a
projection of the second subarea on the main extension plane being
spaced apart from one another. This advantageously enables the
energy or heat to be introduced into multiple areas of the
substrate or the cap which are spaced apart from the access
opening.
[0031] According to one preferred refinement, it is provided that
the introduction of the energy or heat is controlled with the aid
of the laser beam in such a way that the first subarea and the
second subarea are formed essentially rotationally-symmetrically
and essentially in parallel to the surface. This advantageously
enables the energy or heat to be introduced particularly
symmetrically into the substrate or into the cap.
[0032] According to one preferred refinement, it is provided that
the introduction of the energy or heat is controlled with the aid
of the laser beam in such a way that the second laser pulse
expansion area includes further subareas, in particular three or
four or five or six or seven or eight or nine or ten further
subareas, the subareas being formed essentially
rotationally-symmetrically and essentially in parallel to the
surface and being situated essentially rotationally-symmetrically
and essentially in parallel to the surface around the access
opening with the first subarea and the second subarea. This
advantageously enables the energy or heat to be introduced in a
particularly symmetrical and targeted way into the substrate or
into the cap.
[0033] According to one preferred refinement, it is provided that
the introduction of the energy or heat is controlled with the aid
of the laser beam in such a way that the laser beam includes a
laser pulse duration and the laser pulse intensity is provided as
chronologically variable. This advantageously enables energy or
heat to be introduced in a targeted way into the substrate or into
the cap chronologically already before a first transition of the
material area from the solid into the liquid aggregate state and
chronologically after a second transition of the material area from
the liquid into the solid aggregate state. Therefore, as a result
of heat conduction in the substrate or in the cap, this enables
areas of the substrate or the cap adjoining the material area or
the absorbing part of the substrate or the cap to be brought to a
temperature which is elevated in comparison to the related art
chronologically before the first transition and chronologically
after the second transition. The temperature gradients in the
substrate or in the cap, in particular in the area of the access
opening, are therefore reduced in comparison to the related art.
This enables the thermal expansion in the event of a temperature
increase and/or the thermal shrinking in the event of a temperature
reduction of adjacent areas in the substrate or the cap, in
particular in the area of the access opening, to be adapted to one
another, and therefore the mechanical stresses occurring in the
area of the sealed access opening to be reduced in comparison to
the related art.
[0034] A further subject matter of the present invention is a
micromechanical component having a substrate and a cap connected to
the substrate and, together with the substrate, enclosing a first
cavity, a first pressure prevailing and a first gas mixture having
a first chemical composition being enclosed in the first cavity,
the substrate or the cap including a sealed access opening, the
substrate or the cap including a material area which solidifies and
seals the access opening after a controlled introduction of energy
or heat into an absorbing part of the substrate or the cap with the
aid of a laser beam including a spatial laser pulse expansion,
which extends along a surface of the substrate or the cap facing
away from the first cavity and extending essentially in parallel to
a main extension plane of the substrate, and a laser pulse
intensity, to minimize internal stresses in the substrate or the
cap. This advantageously provides a compact, mechanically robust,
and cost-effective micromechanical component having an adjusted
first pressure. The aforementioned advantages of the method
according to the present invention also apply correspondingly to
the micromechanical component according to the present
invention.
[0035] According to one preferred refinement, it is provided that
the substrate or the cap includes silicon. This advantageously
enables the micromechanical component to be manufactured using
standard methods of semiconductor layer technology.
[0036] According to one preferred refinement, it is provided that
the cap, together with the substrate, encloses a second cavity, a
second pressure prevailing and a second gas mixture having a second
chemical composition being enclosed in the second cavity. In this
way, a compact, mechanically robust, and cost-effective
micromechanical component having an adjusted first pressure and
second pressure is advantageously provided.
[0037] According to one preferred refinement, it is provided that
the first pressure is lower than the second pressure, a first
sensor unit for rotation rate measurement being situated in the
first cavity, and a second sensor unit for acceleration measurement
being situated in the second cavity. In this way, a mechanically
robust micromechanical component for rotation rate measurement and
acceleration measurement, having optimal operating conditions for
both the first sensor unit and the second sensor unit, is
advantageously provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] FIG. 1 shows a micromechanical component having an open
access opening according to one exemplary specific embodiment of
the present invention in a schematic representation.
[0039] FIG. 2 shows the micromechanical component according to FIG.
1 having a sealed access opening in a schematic representation.
[0040] FIG. 3 shows a method for manufacturing a micromechanical
component according to one exemplary specific embodiment of the
present invention in a schematic representation.
[0041] FIG. 4 shows a micromechanical component having an open
access opening according to another exemplary specific embodiment
of the present invention in a schematic representation.
[0042] FIG. 5 shows the micromechanical component according to FIG.
4 having a sealed access opening in a schematic representation.
[0043] FIG. 6, FIG. 7, FIG. 8, and FIG. 9 show spatial laser pulse
expansions according to exemplary specific embodiments of the
present invention in schematic representations.
DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS
[0044] Identical parts are denoted by the same reference numerals
in the various figures and are therefore generally also cited or
mentioned only once.
[0045] FIG. 1 and FIG. 2 show schematic representations of a
micromechanical component 1 having an open access opening 11 in
FIG. 1, and having a sealed access opening 11 in FIG. 2, according
to one exemplary specific embodiment of the present invention.
Micromechanical component 1 includes a substrate 3 and a cap 7.
Substrate 3 and cap 7 are, preferably hermetically, connected to
one another and together enclose a first cavity 5. For example,
micromechanical component 1 is designed in such a way that
substrate 3 and cap 7 additionally together enclose a second
cavity. The second cavity, however, is not shown in FIG. 1 and in
FIG. 2.
[0046] For example, a first pressure prevails in first cavity 5, in
particular when access opening 11 is sealed, as shown in FIG. 2.
Moreover, a first gas mixture having a first chemical composition
is enclosed in first cavity 5. In addition, for example, a second
pressure prevails in the second cavity, and a second gas mixture
having a second chemical composition is enclosed in the second
cavity. Access opening 11 is preferably situated in substrate 3 or
in cap 7. In the present exemplary embodiment, access opening 11 is
situated in cap 7 by way of example. According to the present
invention, however, it may also be alternatively provided thereto
that access opening 11 is situated in substrate 3.
[0047] It is provided, for example, that the first pressure in
first cavity 5 is lower than the second pressure in the second
cavity. It is also provided, for example, that a first
micromechanical sensor unit for rotation rate measurement, which is
not shown in FIG. 1 and FIG. 2, is situated in first cavity 5, and
a second micromechanical sensor unit for acceleration measurement,
which is not shown in FIG. 1 and FIG. 2, is situated in the second
cavity.
[0048] FIG. 3 shows a method for manufacturing micromechanical
component 1 according to one exemplary specific embodiment of the
present invention in a schematic representation. In this method,
[0049] in a first method step 101, in particular narrow access
opening 11 connecting first cavity 5 to surroundings 9 of
micromechanical component 1 is formed in substrate 3 or in cap 7.
FIG. 1 shows micromechanical component 1 after first method step
101 by way of example. Moreover, [0050] in a second method step
102, the first pressure and/or the first chemical composition in
first cavity 5 is adjusted, or first cavity 5 is flooded with the
desired gas and the desired internal pressure via the access
channel. Furthermore, for example, [0051] in a third method step
103, access opening 11 is sealed by introducing energy or heat with
the aid of a laser into an absorbing part of substrate 3 or cap 7.
Alternatively, for example, it is also provided that [0052] in
third method step 103, the area around the access channel is
preferably heated only locally by a laser, and the access channel
is hermetically sealed. It is thus advantageously possible to also
provide the method according to the present invention with energy
sources other than with a laser for sealing access opening 11. FIG.
2 shows micromechanical component 1 after third method step 103 by
way of example.
[0053] For example, it is provided that substrate 3 is connected to
cap 7 in a fourth method step, the fourth method step being carried
out before or after first method step 101.
[0054] Chronologically after third method step 103, it is possible
for mechanical stresses to occur in a lateral area 15, shown by way
of example in FIG. 2, on a surface of cap 7 facing away from cavity
5 and in the depth perpendicularly to a projection of lateral area
15 onto the surface, i.e., along access opening 11 and in the
direction of first cavity 5 of micromechanical component 1. These
mechanical stresses, in particular local mechanical stresses,
prevail in particular on and in the vicinity of an interface
between a material area 13 of cap 7, which in third method step 103
enters a liquid aggregate state and after third method step 103
enters a solid aggregate state and seals access opening 11, and a
remaining area of cap 7, which remains in a solid aggregate state
during third method step 103. In FIG. 2, material area 13 of cap 7
sealing access opening 11 is to be regarded only schematically or
is shown only schematically, in particular with respect to its
lateral extension or form, extending in particular in parallel to
the surface, and in particular with respect to its expansion or
configuration perpendicularly to the lateral extension, running in
particular perpendicularly to the surface.
[0055] FIG. 4 and FIG. 5 show a schematic representation of a
micromechanical component 1 having an open access opening 11 in
FIG. 4 and having a sealed access opening 11 in FIG. 5 according to
another exemplary specific embodiment of the present invention. It
is shown by way of example in this case that a first
micromechanical sensor unit for rotation rate measurement 1017 or a
MEMS element is situated in first cavity 5. FIG. 4 and FIG. 5 also
show a main extension plane 100 of substrate 3 by way of example.
In addition, FIG. 5 shows by way of example a surface 1011
extending essentially in parallel to main extension plane 100 and a
laser beam 1005. Furthermore, laser pulse intensities 1003 of laser
beam 1005 are shown by way of example in FIG. 5. FIG. 5 shows a
Gaussian laser pulse intensity 1019 or a Gaussian beam profile and
a uniform or top-hat laser pulse intensity 1021 or a uniform or
top-hat beam profile by way of example.
[0056] It is provided, for example, that spatial intensity profile
or laser pulse intensities 1003 of laser radiation 1005 used for
the sealing process or the third method step are executed in such a
way that internal stresses in the material, which occur in
particular during the cooling process, are minimized.
[0057] It is provided according to the present invention that the
introduction of the energy or heat is controlled with the aid of
laser beam 1005, which includes a spatial laser pulse expansion
1001, which extends essentially along surface 1011 of substrate 3
or cap 7, and laser pulse intensity 1003, to minimize internal
stresses in substrate 3 or in cap 7.
[0058] FIG. 6, FIG. 7, FIG. 8, and FIG. 9 show schematic
representations of spatial laser pulse expansions 1001 according to
exemplary specific embodiments of the present invention. In this
case, FIG. 6 shows a full-area spatial laser pulse expansion 1001
by way of example. FIG. 7, FIG. 8, and FIG. 9 each show lateral
views or sectional views of a partial area of micromechanical
component 1 in the left area and horizontal projections or views of
a plane essentially in parallel to surface 1011 in the right
area.
[0059] Furthermore, it is shown by way of example in FIG. 7 that
spatial laser pulse expansion 1001 includes a first laser pulse
expansion area 1007 having at least one first laser pulse intensity
and a second laser pulse expansion area 1009 having at least one
second laser pulse intensity. In this case, a projection of first
laser pulse expansion area 1007 on main extension plane 100 and a
projection of access opening 11 on main extension plane 100 at
least partially overlap. Furthermore, FIG. 7 shows by way of
example that a projection of first laser pulse expansion area 1007
on main extension plane 100 and a projection of second laser pulse
expansion area 1009 on main extension plane 100 are spaced apart
from one another. In addition, FIG. 7 shows by way of example that
a projection of second laser pulse expansion area 1009 on main
extension plane 100 and a projection of access opening 11 on main
extension plane 100 are spaced apart from one another.
[0060] It is provided in spatial laser pulse expansion 1001 shown
by way of example in FIG. 7, for example, that a first material
area of a first absorbing area of the absorbing part of substrate 3
or cap 7 enters a liquid aggregate state as a result of the first
laser pulse intensity of first laser pulse expansion area 1007, a
second material area of a second absorbing area of the absorbing
part of substrate 3 or cap 7 entering a liquid aggregate state or
remaining in a solid aggregate state as a result of the second
laser pulse intensity of second laser pulse expansion area
1009.
[0061] In other words, it is shown by way of example in FIG. 7 that
in addition to the molten area around the ventilation hole or
material area 13, which is situated in the area of access opening
11, additional areas in the material in the closer or further
surroundings are heated or melted. This is advantageous in
particular because therefore, for example, local compressive
stresses may be generated, which counteract the formation of
tensile stresses in the sealing area or in the immediate area of
access opening 11. For example, a combination of a high first laser
pulse intensity with a high second laser pulse intensity is
provided. For example, second laser pulse expansion area 1009
surrounds the sealing area or access opening 11 in the shape of a
ring or circle at a defined distance. In this case, the second
laser pulse intensity is adjusted in such a way, for example, that
melting does not occur in second laser pulse expansion area 1009,
but rather only heating.
[0062] FIG. 8 shows by way of example that second laser pulse
expansion area 1009 includes a first subarea 1013 and a second
subarea 1015. It is provided in this case, for example, that a
projection of first subarea 1013 on main extension plane 100 and a
projection of second subarea 1015 on main extension plane 100 are
spaced apart from one another. In addition, FIG. 8 shows by way of
example that first subarea 1013 and second subarea 1015 are formed
essentially rotationally-symmetrically or punctiform and
essentially in parallel to surface 1011. Finally, FIG. 8 shows by
way of example that second laser pulse expansion area 1009 includes
six further subareas. It is shown in this case by way of example
that the subareas are formed essentially rotationally symmetrically
or punctiform and essentially in parallel to surface 1011 and are
situated essentially rotationally symmetrical around access opening
11 and essentially in parallel to surface 1011 with first subarea
1013 and with second subarea 1015. In other words, FIG. 8 shows by
way of example that multiple points in the auxiliary area or in
second laser pulse expansion area 1009 are irradiated in a
punctiform way.
[0063] It is also provided according to the present invention, for
example, that first laser pulse expansion area 1007 is a spatial
laser pulse expansion of a first laser beam, and second laser pulse
expansion area 1009 is a spatial laser pulse expansion of a second
laser beam. In addition, it is also provided, for example, that
first subarea 1013 is a spatial laser pulse expansion of a third
laser beam, and second subarea 1015 is a spatial laser pulse
expansion of a fourth laser beam.
[0064] Furthermore, for example, it is provided that the further
subareas are spatial laser pulse expansions of further laser
beams.
[0065] Finally, FIG. 9 shows that spatial laser pulse expansion
1001 is formed as a section area of a hollow cylinder extending
perpendicularly in relation to the longitudinal axis of the hollow
cylinder, the longitudinal axis being essentially coincident with
the center point of access opening 11. For example, FIG. 9 shows in
this case that a high laser intensity or laser pulse intensity 1003
is only applied to substrate 3 or to cap 7 in the sealing area or
in the area of access opening 11, high laser pulse intensity 1003
being situated in a ring shape around the actual ventilation hole
or around access opening 11. For example, such a beam profile is a
doughnut beam profile.
[0066] Spatial laser pulse expansions 1001 shown here are only to
be viewed as examples. According to the present invention,
arbitrarily shaped single or also multiple spatial laser pulse
expansions 1001 are provided, which heat or melt substrate 3 or cap
7 and reduce the local tensile stresses in the sealing area or in
the area of access opening 11 in comparison to the related art.
[0067] For example, it is also provided that to minimize the
stresses, the chronological sequence of the laser irradiation of
substrate 3 or cap 7 in the sealing area or in the area around
access opening 11 and in the auxiliary area or in areas spaced
apart from access opening 11 is controlled suitably.
[0068] Further advantages of the method according to the present
invention and micromechanical component 1 according to the present
invention in relation to the related art may include the following:
[0069] Various sensor cores having different requirements for the
internal pressure may be combined easily on one chip. [0070]
Arbitrary internal pressures, also very low internal pressures, may
be adjusted in a MEMS cavity or in first cavity 5. [0071] Internal
stresses caused by the laser method used are reliably reduced and
the robustness of the components is therefore significantly
increased. [0072] The technology is simple, robust, and
cost-effective. [0073] The manufacturing method is compatible with
the known manufacturing processes, for example, also with capping
processes, for example, with aluminum-germanium (AlGe) eutectic
bonding and with seal glass bonding. [0074] The method according to
the present invention enables a seal of the MEMS cavity which is
particularly stable over the service life.
* * * * *